I finally had a little spare time to work the D2 and found a few things that are not good. The fuel system is very dirty. the filters and filter housing had a lot of black sludge in them. Someone added a primary screen filter under the seat and it was full of sludge also. I dropped the engine oil and found more metal than I would have liked to have seen. The filter was the same way. The metal looked like aluminum or lead to me and the magnet would not stick to it. I am at a crossroads now. Do I pull the blade off and drop the pan and check the rods and mains or do I just do an in-frame and put new pistons, liners, and bearings in it? I have yet to hear this engine run. Should I change the filter and oil and try to get it running and change it again after a couple hours?? Any advice? 
 

Hmmm...If it was mine I'd go completely through it and check everything, with the age on these old engines seals get brittle and O-rings leak around liners,etc,etc,etc.

Hi All,
Dont forget in a D2 the pistons come out the bottom so an in frame rebuild is almost impossible due to the crank in the way.

I would put some new oil and filter and run it for a while keeping in mind to listen for any noises. Also a good idea is to get a long handle screwdriver and place one end on the block and the other end just behind the ear and it is amazing all the sounds you can hear in the block.

Regards

a bit of dowel or broom handle also works as a rough and ready mechanics stethoscope. as long as it stiff it will conduct sound. a proper stethoscope isnt expensive either.

neil he said it wasnt magnetic so i doubt its the timing gears as there all steel are they not? that doesnt mean theres not a bushing somewhere failing.

Thank you for the advice guys. I was not aware the pistons came out the bottom. This is about 30 years older than any other Cat I have worked on. Still trying to get my hands on a service manual for it.

Pricey, but they are out there...
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Hi all,
You can pull the pistons out thru the bottom with the crank still in as I've done it with my D2 5U16437 as I changed no 2 and no 3 pistons while the engine was still in the machine but to remove no 3 piston I had to remove the oil pump and they go back in easy enough without using a ring compressor.
Cheers Wayne 👍

Another method I've used is to re-install the pistons through the bottom but without the rings on the pistons... then raise the pistons above the block, install the rings, and then push the pistons into the block with a ring compressor as you would any other engine. Seemed easier than trying to compress the rings with my finger tips when putting them in from the bottom.

This is from the Servicemen Reference Book for D311/D2